glob (programming)

In computer programming, glob patterns specify sets of filenames with wildcard characters. For example, the Unix Bash shell command mv *.txt textfiles/ moves (mv) all files with names ending in .txt from the current directory to the directory textfiles. Here, * is a wildcard standing for "any string of characters" and *.txt is a glob pattern. The other common wildcard is the question mark (?), which stands for one character.

A screenshot of the original 1971 Unix reference page for glob – note the owner is dmr, short for Dennis Ritchie.

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The glob command, short for global, originates in the earliest versions of Bell Labs' Unix[1]. The command interpreters of the early versions of Unix (1st through 6th Editions, 1969–75) relied on a separate program to expand wildcard characters in unquoted arguments to a command: /etc/glob. That program performed the expansion and supplied the expanded list of file paths to the command for execution.

Later, this functionality was provided as a library function, glob(), used by programs such as the shell.

The Bash shell also supports Extended Globbing which allows other pattern matching operators to be used to match multiple occurrences of a pattern enclosed in parentheses. It can be enabled by setting the extglob shell option.[4]

The SQL LIKE operator has an equivalent of ? and *. There is no equivalent of […].

Common wildcard

SQL wildcard

?

_

*

%

Standard SQL uses a glob-like syntax for simple string matching in its LIKE operator. The percent sign (%) matches zero or more characters, and the underscore matches exactly one character. The term "glob" is not generally used in the SQL community, however. Many implementations of SQL have extended the LIKE operator to allow a richer pattern-matching language incorporating elements of regular expressions.

Some proprietary extensions such as Transact-SQL provide the […] functionality, e.g., [characters] and [^characters].[6]

Globs attempt to match the entire string (for example, S*.DOC matches S.DOC and SA.DOC, but not POST.DOC or SURREY.DOCKS), whereas regular expressions match a substring unless the expression is enclosed with ^ and $ (so the equivalent of S*.DOC is ^S.*\.DOC$[7]).

Java has a Files class containing methods that operate on glob patterns.[18]

Haskell has a Glob package with the main module System.FilePath.Glob. The pattern syntax is based on a subset of Zsh’s. It tries to optimize the given pattern and should be noticeably faster than a naïve character-by-character matcher.[19]

Perl has both a glob function (as discussed in Larry Wall's book Programming Perl) and a Glob extension which mimics the BSD glob routine.[20] Perl's angle brackets can be used to glob as well: <*.log>.

Python has a glob module in the standard library which performs wildcard pattern matching on filenames,[22] and an fnmatch module with functions for matching strings or filtering lists based on these same wildcard patterns[23]Guido van Rossum, author of the Python programming language, wrote and contributed a glob routine to BSDUnix in 1986.[24] There were previous implementations of glob, e.g., in the ex and ftp programs in previous releases of BSD.

Ruby has a glob method for the Dir class which performs wildcard pattern matching on filenames.[25] Several libraries such as Rant and Rake provide a FileList class which has a glob method or use the method FileList.[] identically.